The glider contacted trees while on final approach to land. The pilot reported the accident occurred during his second flight of the day. He reported that he checked the winds prior to takeoff and that the flight was bumpy up to 2,000 feet above ground level (agl) at which point it smoothed out to 3,000 feet agl where he was released from the tow plane. He stated that after a 15 minute flight he returned to the airport where he entered a left hand traffic pattern at 1,000 feet agl for runway 18. The pilot reported that when he entered the traffic pattern he noticed the wind sock was shifting and the glider was losing altitude at a rate that was faster than the previous flight. He stated that because of this, he turned onto base leg sooner than normal. He reported, "Upon turning there was an immediate sense of an inability to penetrate thru the airmass as the glider continued to lose altitude." He stated he lowered the nose of the glider in an attempt to gain airspeed and flew an abbreviated base leg, heading straight for the runway. The pilot reported he then noted a shift in the wind and the glider descended into the 75 foot tall trees northeast of the approach end of the runway. The pilot of the tow plane reported he flew four flights on the day of the accident. He stated that during the first three flights the winds were from the southwest at less than 15 knots. He reported that for the accident flight the windsock indicated the winds were from the southeast and that the automated weather observing system (AWOS) indicated the winds were from 170 degrees at 8 or 9 knots. He stated that after he landed the windsock indicated the winds had shifted again to the southwest. He stated he checked the AWOS from the Mason-Jewett Airport (TEW), Mason, Michigan, and it was indicating the winds were variable from 160 to 240 degrees at 9 knots gusting to 16 or 20 knots. He reported that this was at the same time that the glider was in the traffic pattern to land. The winds rpeorted at TEW, located 20 miles west-northwest of the accident site at 1317 were from 200 degrees at 5 knots gusting to 14 knots. Twenty minutes prior, the TEW winds were reported as being from 200 degrees at 5 knots. The winds reported at the Howell-Livingston County Airport (OZW), Howell, Michigan, located 15 miles north-northeast of the accident site at 1317 were from 170 degrees at 9 knots. Twenty minutes later the OZW winds had shifted to 200 degrees at 10 knots gusting to 15 knots.